The present invention relates, in general, to an improved, more durable diffuser tip to diffuse light from a light-emitting end of an optical fiber. More particularly, the invention relates to a diffuser which includes a decladded optical fiber core which is covered by a protective coating and an optical coupling layer wherein the protective coating has an index of refraction between the indices of refraction of the core and the optical coupling layer while at the same time the protective coating increases the bending moment required to break the core. The protective coating is made of polymethyl methacrylate or methylpentene.
Surgeons commonly use lasers to treat benign prostatic hyperplasia, or BPH. BPH is a condition of an enlarged prostate gland. The prostate gland with BPH typically increases in size to between about two and four times normal. The lasers used to treat it must have durable diffuser tips that distribute light radially in a predictable manner and bend without breaking. Small diffuser tips offer an advantage to the surgeon as well. Builders of these diffuser tips commonly make them from optical fibers and desire to make them small.
An optical fiber typically contains a glass core surrounded by cladding and a jacket. The cladding protects the inherently weaker glass core by lending mechanical support to the core. The cladding also has an index of refraction lower than that of the core to block light from emerging radially from the core.
A prior art diffuser tip based on art taught by Esch in U.S. Pat. No. 5,754,717 is shown in FIG. 1. This figure shows a prior art diffuser tip comprised of the stripped core of a typical optical fiber, an optical coupling layer, and a sleeve. The optical coupling layer, replacing the cladding of the optical fiber, has an index of refraction exceeding that of the core to pull the light out of the core using well known physical principles. The sleeve, which surrounds the optical coupling layer, has an index of refraction lower than the optical coupling layer and includes barium sulfate particles to help scatter the light. In order to allow light to pass through the boundary between the optical coupling layer and the sleeve, the inner diameter of the sleeve is abraded. Abrading the surface of the sleeve presents surfaces more nearly normal to the light coming through the optical coupling layer so that the light passes into the sleeve. By controlling the extent of the abrasions, the light intensity as a function of the position along the axis of the sleeve can also be controlled. Designers often prefer an even distribution of light for applications involving BPH.
A diffuser tip taught by Khoury in U.S. Pat. No. 5,151,096 comprises a layer of medical grade epoxy over the core. Medical grade epoxy has an index of refraction higher than that of silicone and so cannot be used in an application having a silicone optical coupling layer.
The process of making the diffuser tip illustrated in FIG. 1 involves stripping a portion of the optical fiber cladding layer away from the optical fiber core. The sleeve is then filled with an appropriate material such as silicone and the declad portion of the core is inserted into the sleeve. Since the cladding layer provides structural support for the core, stripping it away makes the declad portion of the optical fiber core more susceptible to cracking or breaking when it is bent. The problem of cracking or breaking becomes more acute as the diameter of the optical fiber core becomes smaller. While the optical coupling layer and sleeve protect the declad portion of the optical fiber core, the support provided is not as great as the support provided by the cladding layer. It would, therefore, be advantageous to design a diffuser tip wherein the resistance of the declad core to cracking or breaking is improved. It would further be advantageous to design a more resilient diffuser tip without substantially changing the light emitting properties of current designs.
One embodiment of the present invention includes a diffuser tip fashioned from an optical cable""s stripped glass core surrounded by a durable protective coating of acrylic and an optical coupling layer. A Teflon sleeve impregnated with barium sulfate covers the optical coupling layer. The optical coupling layer transfers the light from the protective coating through to the sleeve. The index of refraction of the protective coating exceeds that of the core to couple light from the core by well-known physical principles. The index of refraction of the optical coupling layer exceeds that of the protective coating to couple the light from the protective coating to the sleeve. The material of the protective coating, by enhancing the strength of the declad core while effectively coupling light out of the core to the optical coupling layer, results in an operative diffuser tip that increases the bending moment at which the declad core breaks. In a particular embodiment of the invention the coating comprises polymethyl methacrylate. In a further embodiment of the invention the coating comprises methylpentene.
In a further embodiment of the invention the inner surface of the sleeve is abraded to couple light from the optical coupling layer into the sleeve. The sleeve""s index of refraction is lower than the index of refraction of the optical coupling layer. The abrasion scatters the light rays to allow them to pass into the sleeve when the light rays travel from a layer of higher refractive index to a layer of lower refractive index.